The present invention generally relates to apparatus and methods for treatment of airstreams in an Environmental Control System (ECS) to remove contaminants.
ECSs of various types and complexity are used in military and civil airplanes, helicopter, Mass Transit, Low Speed and High Speed Rail, and spacecraft applications. If fact, environmental control systems in buildings that manage energy consumption operate their systems by controlling contaminant levels or bringing in outside air to dilute contaminants, and require sensors for this process. In aircraft for example, airflow may be circulated to occupied compartments, cargo compartments, and electronic equipment bays. Air containing many pollutants such as particulate matter, aerosols, and hydrocarbons may range in humidity from dry (<2%) to very humid and may be delivered in a heated condition to the cabin from the ECS.
Occupants are not exposed to a single chemical in isolation, and the effects of co-exposures to multiple chemicals are poorly understood. Exposure duration for occupants can be 14+ hours. Air Crews can routinely be assigned to work up to a 16 hour duty day. The duty day can be extended up to the 16 hour limit if there is a maintenance delay or weather. Some international crews are assigned to work a longer duty day. Pilots are limited to flying no more than 100 hours per month, while cabin crew may work up to around 120 hours per month. There are flight safety and security implications for not adequately protecting pilots (who must perform cognitively-demanding safety-sensitive flight duties) and cabin crew (who must maintain cabin safety and security). Specifically, manufacturers are currently required to ensure that aircraft systems are designed to provide—in operation, under normal conditions and during any probable failure—“a sufficient amount of uncontaminated air to enable the crewmembers to perform their duties without undue discomfort or fatigue, and to provide reasonable passenger comfort.” It has been widely recognized by air accident investigators, regulators, and pilot groups that flight safety can be compromised when pilots are exposed to oil-based contaminants in the ventilation air entering from outside the aircraft through the main engine bleeds or APU bleed or other air sources including ground supplies and electric compressors. Requiring pilots to rely on their noses to identify the presence and location of bleed air contaminants prolongs the exposure for the pilots and/or cabin occupants, depending on the location of the contaminant source.
Buildings and high density ground transit have similar concerns and constraints as aircraft.
Metal oxide and other kinds of sensors are generic in response when operated with a constant supply voltage and current at a constant environmental response. It is not possible to determine in a steady state operation mode what VOC contaminant might be present. At times it would be useful in a controlled environment when there are only a few major sources of VOC to be able to identify which VOC is being detected.
It is known that increasing or decreasing metal oxide sensor voltage may change the sensor response to a specific chemical. There may be many compounds present in a more closed environment such as an aircraft cabin or an office, or home. However, only a limited number of volatile organic compounds present are of concern. Ethanol may be present in higher concentrations in closed environments, but is not a significant concern from a control perspective, because it is present in significant quantities in alcoholic beverages. Formaldehyde, acetaldehyde, acrolein, and other aldehydes, on the other hand, are very irritating in low concentrations.
During a flight cycle, the air may have more organic contaminants at ground level through top of climb. It is more likely during these flight stages to sense aldehydes than during cruise phase. During meal service, on the other hand, there may be little to no formaldehyde, but large quantities of alcohol.
As can be seen, there may be an ongoing need to identify the presence of certain VOC's and then enable corrective action to an ECS.